One more question... Can " i = i.6_18;" be sinked out of loop, because it doesn't have memory dependence with others?
Thanks, -Jiangning > -----Original Message----- > From: gcc-ow...@gcc.gnu.org [mailto:gcc-ow...@gcc.gnu.org] On Behalf Of > Jiangning Liu > Sent: Thursday, November 24, 2011 2:57 PM > To: gcc@gcc.gnu.org > Subject: RE: A case exposing code sink issue > > Sorry, I realize we can't do that optimization because a_p may have > dependence upon other memory accesses like MEM[(int *)&a][D.2248_7]. > > For example, if it happens a_p equals &a_p, that optimization would be > wrong. > > But can alias analysis solve the problem if we can guarantee (i+(1<<k)) > is > less than the upbound of array a's definition? > > Or is there any GCC command line switch assuming no array bound > overflow? > That way we can do more aggressive optimizations, right? > > Thanks, > -Jiangning > > > -----Original Message----- > > From: gcc-ow...@gcc.gnu.org [mailto:gcc-ow...@gcc.gnu.org] On Behalf > Of > > Jiangning Liu > > Sent: Thursday, November 24, 2011 12:05 PM > > To: gcc@gcc.gnu.org > > Subject: A case exposing code sink issue > > > > Hi, > > > > For this small test case, > > > > int a[512] ; > > int b[512] ; > > int *a_p ; > > int *b_p ; > > int i ; > > int k ; > > > > int f(void) > > { > > for( k = 1 ; k <= 9 ; k++) > > { > > for( i = k ; i < 512 ; i += k) > > { > > a_p = &a[i + (1<<k)] ; > > b_p = &b[i + (1<<k)] ; > > *a_p = 7 ; > > *b_p = 7 ; > > } > > } > > } > > > > Before sink pass we have, > > > > f () > > { > > int pretmp.11; > > int k.7; > > int i.6; > > int * b_p.3; > > int * a_p.2; > > int D.2248; > > int i.1; > > int D.2246; > > int k.0; > > > > <bb 2>: > > k = 1; > > > > <bb 3>: > > # k.0_9 = PHI <k.7_20(11), 1(2)> > > i = k.0_9; > > if (k.0_9 <= 511) > > goto <bb 7>; > > else > > goto <bb 8>; > > > > <bb 8>: > > Invalid sum of incoming frequencies 900, should be 81 > > goto <bb 5>; > > > > <bb 7>: > > pretmp.11_19 = 1 << k.0_9; > > > > <bb 4>: > > # i.1_34 = PHI <i.6_18(9), k.0_9(7)> > > D.2246_5 = pretmp.11_19; > > D.2248_7 = i.1_34 + D.2246_5; > > a_p.2_8 = &a[D.2248_7]; > > a_p = a_p.2_8; > > b_p.3_13 = &b[D.2248_7]; > > b_p = b_p.3_13; > > MEM[(int *)&a][D.2248_7] = 7; > > MEM[(int *)&b][D.2248_7] = 7; > > i.6_18 = k.0_9 + i.1_34; > > i = i.6_18; > > if (i.6_18 <= 511) > > goto <bb 9>; > > else > > goto <bb 8>; > > > > <bb 9>: > > goto <bb 4>; > > > > <bb 5>: > > Invalid sum of incoming frequencies 81, should be 900 > > k.7_20 = k.0_9 + 1; > > k = k.7_20; > > if (k.7_20 <= 9) > > goto <bb 11>; > > else > > goto <bb 6>; > > > > <bb 11>: > > goto <bb 3>; > > > > <bb 6>: > > return; > > > > } > > > > Can the following statements be sinked out of loop? I don't see this > > optimization happen in trunk. The consequence is register pressure > > increased > > and a spill/fill occurs in RA. > > > > a_p.2_8 = &a[D.2248_7]; > > a_p = a_p.2_8; > > b_p.3_13 = &b[D.2248_7]; > > b_p = b_p.3_13; > > > > I know the sink would happen in sink pass if a_p and b_p are local > > variables. > > > > If this is the root cause, which optimization pass in GCC take the > role > > to > > sink them out of loop? How should we get it fixed? > > > > Thanks, > > -Jiangning > > > > > > > > > >
